The present invention relates to a system for attenuation of noise for use with sound receiving devices. More particularly, the present invention is concerned with a system for attenuating acoustic background sounds in devices employing a microphone for receiving and utilizing sound waves applied thereto.
As experienced by many, background sounds, which will be referred to hereinafter as "noise", in accordance with the commonly acceptable definition thereof, which is "undesired sound", are very disturbing when, for example, conducting a telephone conversation from outdoor telephone booths or when using a microphone to broadcast information from outside premises, such as sports fields or arenas, and other like locations.
There are known in the art several techniques for noise suppression. The first one utilizes a special construction of a microphone providing different sensitivities to sound waves, reaching the microphone from different directions. Such microphones, known as directional microphones, suffer, however, from the obvious disadvantage of not being able to provide a satisfactory solution to sound received from directions other than the two preset, very distinct directions.
Another known noise cancelling technique utilizes electronic generation of "anti-noise" signals precisely out of phase with the incoming noise signals. This technique involves digital processing of sound signals and the irradiation of noise signals into space, out of phase with the phase of the incoming noise signals, so as to cancel out only the incoming noise signals.
A more common noise cancellation technique employs several individual microphones disposed in spaced-apart relationship producing output signals corrresponding to the sound picked up thereby, which signals are then processed and delayed in different ways to obtain an improved signal to noise ratio. This technique is also quite involved and necessitates special equipment.